Microelectromechanical systems (MEMS) are small, movable, mechanical structures built using well-characterized, semi-conductor processes. Advantageously, MEMS can be provided as actuators, which have proven to be very useful in many applications.
Present-day MEMS actuators quite small, having a length of only a few hundred microns, and a width of only a few tens of microns. Such MEMS actuators are typically configured and disposed in a cantilever fashion. In other words, they have an end attached to a substrate and an opposite free end which is movable between at least two positions, one being a neutral position and the others being deflected positions.
Electrostatic, magnetic, piezo and thermal actuation mechanisms are among the most common actuation mechanisms employed MEMS. Of particular importance is the thermal actuation mechanism.
As is understood by those skilled in the art, the deflection of a thermal MEMS actuator results from a potential being applied between a pair of terminals, called “anchor pads”, which potential causes a current flow elevating the temperature of the structure. This elevated temperature ultimately causes a part thereof to contract or elongate, depending on the material being used.
One possible use for MEMS actuators is to configure them as switches. These switches are made of at least one actuator. In the case of multiple actuators, they are typically operated in sequence so as to connect or release one of their parts to a similar part on the other. These actuators form a switch which can be selectively opened or closed using a control voltage applied between corresponding anchor pads on each actuator.
MEMS switches have many advantages. Among other things, they are very small and relatively inexpensive—depending on the configuration. Because they are extremely small, a very large number of MEMS switches can be provided on a single wafer.
Of further advantage, MEMS switches consume minimal electrical power and their response time(s) are extremely short. Impressively, a complete cycle of closing or opening a MEMS switch can be as short as a few milliseconds.
Although prior-art MEMS actuators and switches have proven to be satisfactory to some degree, there nevertheless remains a general need to further improve their performance, reliability and manufacturability. For instance, one factor which generally increases the overall costs of a system using MEMS switches is the inclusion of any additional protection that is oftentimes required in particular markets.
One such type of additional protection that raises the cost of a MEMS based system is a current limiter device. These current limiters are external devices that protect each MEMS switch from being damaged by a relatively large current peak occurring in one of the circuits. Such current peaks—while usually brief in length—can damage unprotected MEMS switches. Eliminating the need for numerous current limiters in MEMS based systems would significantly decrease the overall costs of these systems and represent a significant advance in the art.